1. Field of the Invention
The present invention relates to a horizontal rotary hook of a sewing machine provided with an inner rotary hook and an outer rotary hook respectively made of synthetic resin wherein the inner rotary hook is pulled toward the outer rotary hook by the magnetic force of a thin plate-shaped magnet piece.
2. Description of Prior Art
Conventionally, horizontal rotary hooks offering simple and handy bobbin exchange have been widely used. Such types of horizontal rotary hooks are provided with an outer rotary hook formed with a race surface and an inner rotary hook housing a bobbin retained rotatably in relative to the race surface. The outer rotary hook is rotated in a predetermined direction by a sewing machine motor or the like.
The inner rotary hook is made of a synthetic resin to achieve reduction of weight and manufacturing cost. Also, in recent years, the outer rotary hook is also made of a synthetic resin. Such being the case, various types of horizontal rotary hooks using magnets have been proposed to prevent the inner rotary hook from floating up with respect to the outer rotary hook during sewing work. For example, JP-Y1-1989-54784 discloses a horizontal rotary hook having an outer rotary hook embedded with a thin ring-shaped magnet in the inner bottom surface thereof as well as having an inner rotary hook with the outer bottom surface almost entirely covered with a metal material which is attracted by the magnet.
However, a simple provision of a magnet in the outer rotary hook made of synthetic resin would limit the magnet to a relatively small size, consequently providing insufficient attraction with respect to the inner rotary hook. As a result, the floating of the inner rotary hook is not prevented effectively. Such being the case, mounting of a large type magnet generating strong magnetic force on the outer rotary hook is a possible alternative; however, such countermeasures give rise to problems such as cost and size increase of the horizontal rotary hook. In the outer rotary hook made of synthetic resin, the magnet needs to be fixed to the bottom surface of the outer rotary hook by an adhesive agent or a two-sided adhesive tape. However, this will result in complicated assembly work and furthermore, since the magnet is of small size, consequently having small adhesion area incapable of providing enough adhesion, problems have occurred where the magnet fell off while in use.